The invention relates to an apparatus and method for detecting overlapping objects, in particular mail items.
It is known that mail items, in particular letters, can be sorted by machine, wherein individual mail items are withdrawn from stacks of mail items to separate them. To determine whether, for example, two or more mail items have been drawn from the stack instead of a single mail item, a light source of a detector is used to illuminate the underside of the mail item once it has been drawn down and to produce an image of this. The image is used to check whether the mail item has a single edge or a number of edges, in order to decide whether there is a single mail item or a number of, for example, adhering mail items, hereinafter referred to as a double withdrawal, since individual mail items normally only have a single edge.
If a separated mail item has a number of mail items, it is not always an erroneous double withdrawal, but may be, for example, a reply slip to be attached to a mail item. Similarly, a single mail item may have peripheral lines so that the image appears to show a number of edges.
The known separation methods therefore have the disadvantage that it cannot always be reliably decided whether there is a single mail item or a number of mail items, which have been withdrawn from the stack as a double withdrawal.